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| 1 | +// SPDX-License-Identifier: GPL-2.0-or-later |
| 2 | +/* |
| 3 | + * Copyright 2024- IBM Corp. |
| 4 | + * |
| 5 | + * X25519 scalar multiplication with 51 bits limbs for PPC64le. |
| 6 | + * Based on RFC7748 and AArch64 optimized implementation for X25519 |
| 7 | + * - Algorithm 1 Scalar multiplication of a variable point |
| 8 | + */ |
| 9 | + |
| 10 | +#include <crypto/curve25519.h> |
| 11 | +#include <crypto/internal/kpp.h> |
| 12 | + |
| 13 | +#include <linux/types.h> |
| 14 | +#include <linux/jump_label.h> |
| 15 | +#include <linux/kernel.h> |
| 16 | +#include <linux/module.h> |
| 17 | +#include <linux/scatterlist.h> |
| 18 | + |
| 19 | +#include <linux/cpufeature.h> |
| 20 | +#include <linux/processor.h> |
| 21 | + |
| 22 | +typedef uint64_t fe51[5]; |
| 23 | + |
| 24 | +asmlinkage void x25519_fe51_mul(fe51 h, const fe51 f, const fe51 g); |
| 25 | +asmlinkage void x25519_fe51_sqr(fe51 h, const fe51 f); |
| 26 | +asmlinkage void x25519_fe51_mul121666(fe51 h, fe51 f); |
| 27 | +asmlinkage void x25519_fe51_sqr_times(fe51 h, const fe51 f, int n); |
| 28 | +asmlinkage void x25519_fe51_frombytes(fe51 h, const uint8_t *s); |
| 29 | +asmlinkage void x25519_fe51_tobytes(uint8_t *s, const fe51 h); |
| 30 | +asmlinkage void x25519_cswap(fe51 p, fe51 q, unsigned int bit); |
| 31 | + |
| 32 | +#define fmul x25519_fe51_mul |
| 33 | +#define fsqr x25519_fe51_sqr |
| 34 | +#define fmul121666 x25519_fe51_mul121666 |
| 35 | +#define fe51_tobytes x25519_fe51_tobytes |
| 36 | + |
| 37 | +static void fadd(fe51 h, const fe51 f, const fe51 g) |
| 38 | +{ |
| 39 | + h[0] = f[0] + g[0]; |
| 40 | + h[1] = f[1] + g[1]; |
| 41 | + h[2] = f[2] + g[2]; |
| 42 | + h[3] = f[3] + g[3]; |
| 43 | + h[4] = f[4] + g[4]; |
| 44 | +} |
| 45 | + |
| 46 | +/* |
| 47 | + * Prime = 2 ** 255 - 19, 255 bits |
| 48 | + * (0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffed) |
| 49 | + * |
| 50 | + * Prime in 5 51-bit limbs |
| 51 | + */ |
| 52 | +static fe51 prime51 = { 0x7ffffffffffed, 0x7ffffffffffff, 0x7ffffffffffff, 0x7ffffffffffff, 0x7ffffffffffff}; |
| 53 | + |
| 54 | +static void fsub(fe51 h, const fe51 f, const fe51 g) |
| 55 | +{ |
| 56 | + h[0] = (f[0] + ((prime51[0] * 2))) - g[0]; |
| 57 | + h[1] = (f[1] + ((prime51[1] * 2))) - g[1]; |
| 58 | + h[2] = (f[2] + ((prime51[2] * 2))) - g[2]; |
| 59 | + h[3] = (f[3] + ((prime51[3] * 2))) - g[3]; |
| 60 | + h[4] = (f[4] + ((prime51[4] * 2))) - g[4]; |
| 61 | +} |
| 62 | + |
| 63 | +static void fe51_frombytes(fe51 h, const uint8_t *s) |
| 64 | +{ |
| 65 | + /* |
| 66 | + * Make sure 64-bit aligned. |
| 67 | + */ |
| 68 | + unsigned char sbuf[32+8]; |
| 69 | + unsigned char *sb = PTR_ALIGN((void *)sbuf, 8); |
| 70 | + |
| 71 | + memcpy(sb, s, 32); |
| 72 | + x25519_fe51_frombytes(h, sb); |
| 73 | +} |
| 74 | + |
| 75 | +static void finv(fe51 o, const fe51 i) |
| 76 | +{ |
| 77 | + fe51 a0, b, c, t00; |
| 78 | + |
| 79 | + fsqr(a0, i); |
| 80 | + x25519_fe51_sqr_times(t00, a0, 2); |
| 81 | + |
| 82 | + fmul(b, t00, i); |
| 83 | + fmul(a0, b, a0); |
| 84 | + |
| 85 | + fsqr(t00, a0); |
| 86 | + |
| 87 | + fmul(b, t00, b); |
| 88 | + x25519_fe51_sqr_times(t00, b, 5); |
| 89 | + |
| 90 | + fmul(b, t00, b); |
| 91 | + x25519_fe51_sqr_times(t00, b, 10); |
| 92 | + |
| 93 | + fmul(c, t00, b); |
| 94 | + x25519_fe51_sqr_times(t00, c, 20); |
| 95 | + |
| 96 | + fmul(t00, t00, c); |
| 97 | + x25519_fe51_sqr_times(t00, t00, 10); |
| 98 | + |
| 99 | + fmul(b, t00, b); |
| 100 | + x25519_fe51_sqr_times(t00, b, 50); |
| 101 | + |
| 102 | + fmul(c, t00, b); |
| 103 | + x25519_fe51_sqr_times(t00, c, 100); |
| 104 | + |
| 105 | + fmul(t00, t00, c); |
| 106 | + x25519_fe51_sqr_times(t00, t00, 50); |
| 107 | + |
| 108 | + fmul(t00, t00, b); |
| 109 | + x25519_fe51_sqr_times(t00, t00, 5); |
| 110 | + |
| 111 | + fmul(o, t00, a0); |
| 112 | +} |
| 113 | + |
| 114 | +static void curve25519_fe51(uint8_t out[32], const uint8_t scalar[32], |
| 115 | + const uint8_t point[32]) |
| 116 | +{ |
| 117 | + fe51 x1, x2, z2, x3, z3; |
| 118 | + uint8_t s[32]; |
| 119 | + unsigned int swap = 0; |
| 120 | + int i; |
| 121 | + |
| 122 | + memcpy(s, scalar, 32); |
| 123 | + s[0] &= 0xf8; |
| 124 | + s[31] &= 0x7f; |
| 125 | + s[31] |= 0x40; |
| 126 | + fe51_frombytes(x1, point); |
| 127 | + |
| 128 | + z2[0] = z2[1] = z2[2] = z2[3] = z2[4] = 0; |
| 129 | + x3[0] = x1[0]; |
| 130 | + x3[1] = x1[1]; |
| 131 | + x3[2] = x1[2]; |
| 132 | + x3[3] = x1[3]; |
| 133 | + x3[4] = x1[4]; |
| 134 | + |
| 135 | + x2[0] = z3[0] = 1; |
| 136 | + x2[1] = z3[1] = 0; |
| 137 | + x2[2] = z3[2] = 0; |
| 138 | + x2[3] = z3[3] = 0; |
| 139 | + x2[4] = z3[4] = 0; |
| 140 | + |
| 141 | + for (i = 254; i >= 0; --i) { |
| 142 | + unsigned int k_t = 1 & (s[i / 8] >> (i & 7)); |
| 143 | + fe51 a, b, c, d, e; |
| 144 | + fe51 da, cb, aa, bb; |
| 145 | + fe51 dacb_p, dacb_m; |
| 146 | + |
| 147 | + swap ^= k_t; |
| 148 | + x25519_cswap(x2, x3, swap); |
| 149 | + x25519_cswap(z2, z3, swap); |
| 150 | + swap = k_t; |
| 151 | + |
| 152 | + fsub(b, x2, z2); // B = x_2 - z_2 |
| 153 | + fadd(a, x2, z2); // A = x_2 + z_2 |
| 154 | + fsub(d, x3, z3); // D = x_3 - z_3 |
| 155 | + fadd(c, x3, z3); // C = x_3 + z_3 |
| 156 | + |
| 157 | + fsqr(bb, b); // BB = B^2 |
| 158 | + fsqr(aa, a); // AA = A^2 |
| 159 | + fmul(da, d, a); // DA = D * A |
| 160 | + fmul(cb, c, b); // CB = C * B |
| 161 | + |
| 162 | + fsub(e, aa, bb); // E = AA - BB |
| 163 | + fmul(x2, aa, bb); // x2 = AA * BB |
| 164 | + fadd(dacb_p, da, cb); // DA + CB |
| 165 | + fsub(dacb_m, da, cb); // DA - CB |
| 166 | + |
| 167 | + fmul121666(z3, e); // 121666 * E |
| 168 | + fsqr(z2, dacb_m); // (DA - CB)^2 |
| 169 | + fsqr(x3, dacb_p); // x3 = (DA + CB)^2 |
| 170 | + fadd(b, bb, z3); // BB + 121666 * E |
| 171 | + fmul(z3, x1, z2); // z3 = x1 * (DA - CB)^2 |
| 172 | + fmul(z2, e, b); // z2 = e * (BB + (DA + CB)^2) |
| 173 | + } |
| 174 | + |
| 175 | + finv(z2, z2); |
| 176 | + fmul(x2, x2, z2); |
| 177 | + fe51_tobytes(out, x2); |
| 178 | +} |
| 179 | + |
| 180 | +void curve25519_arch(u8 mypublic[CURVE25519_KEY_SIZE], |
| 181 | + const u8 secret[CURVE25519_KEY_SIZE], |
| 182 | + const u8 basepoint[CURVE25519_KEY_SIZE]) |
| 183 | +{ |
| 184 | + curve25519_fe51(mypublic, secret, basepoint); |
| 185 | +} |
| 186 | +EXPORT_SYMBOL(curve25519_arch); |
| 187 | + |
| 188 | +void curve25519_base_arch(u8 pub[CURVE25519_KEY_SIZE], |
| 189 | + const u8 secret[CURVE25519_KEY_SIZE]) |
| 190 | +{ |
| 191 | + curve25519_fe51(pub, secret, curve25519_base_point); |
| 192 | +} |
| 193 | +EXPORT_SYMBOL(curve25519_base_arch); |
| 194 | + |
| 195 | +static int curve25519_set_secret(struct crypto_kpp *tfm, const void *buf, |
| 196 | + unsigned int len) |
| 197 | +{ |
| 198 | + u8 *secret = kpp_tfm_ctx(tfm); |
| 199 | + |
| 200 | + if (!len) |
| 201 | + curve25519_generate_secret(secret); |
| 202 | + else if (len == CURVE25519_KEY_SIZE && |
| 203 | + crypto_memneq(buf, curve25519_null_point, CURVE25519_KEY_SIZE)) |
| 204 | + memcpy(secret, buf, CURVE25519_KEY_SIZE); |
| 205 | + else |
| 206 | + return -EINVAL; |
| 207 | + return 0; |
| 208 | +} |
| 209 | + |
| 210 | +static int curve25519_generate_public_key(struct kpp_request *req) |
| 211 | +{ |
| 212 | + struct crypto_kpp *tfm = crypto_kpp_reqtfm(req); |
| 213 | + const u8 *secret = kpp_tfm_ctx(tfm); |
| 214 | + u8 buf[CURVE25519_KEY_SIZE]; |
| 215 | + int copied, nbytes; |
| 216 | + |
| 217 | + if (req->src) |
| 218 | + return -EINVAL; |
| 219 | + |
| 220 | + curve25519_base_arch(buf, secret); |
| 221 | + |
| 222 | + /* might want less than we've got */ |
| 223 | + nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len); |
| 224 | + copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, |
| 225 | + nbytes), |
| 226 | + buf, nbytes); |
| 227 | + if (copied != nbytes) |
| 228 | + return -EINVAL; |
| 229 | + return 0; |
| 230 | +} |
| 231 | + |
| 232 | +static int curve25519_compute_shared_secret(struct kpp_request *req) |
| 233 | +{ |
| 234 | + struct crypto_kpp *tfm = crypto_kpp_reqtfm(req); |
| 235 | + const u8 *secret = kpp_tfm_ctx(tfm); |
| 236 | + u8 public_key[CURVE25519_KEY_SIZE]; |
| 237 | + u8 buf[CURVE25519_KEY_SIZE]; |
| 238 | + int copied, nbytes; |
| 239 | + |
| 240 | + if (!req->src) |
| 241 | + return -EINVAL; |
| 242 | + |
| 243 | + copied = sg_copy_to_buffer(req->src, |
| 244 | + sg_nents_for_len(req->src, |
| 245 | + CURVE25519_KEY_SIZE), |
| 246 | + public_key, CURVE25519_KEY_SIZE); |
| 247 | + if (copied != CURVE25519_KEY_SIZE) |
| 248 | + return -EINVAL; |
| 249 | + |
| 250 | + curve25519_arch(buf, secret, public_key); |
| 251 | + |
| 252 | + /* might want less than we've got */ |
| 253 | + nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len); |
| 254 | + copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, |
| 255 | + nbytes), |
| 256 | + buf, nbytes); |
| 257 | + if (copied != nbytes) |
| 258 | + return -EINVAL; |
| 259 | + return 0; |
| 260 | +} |
| 261 | + |
| 262 | +static unsigned int curve25519_max_size(struct crypto_kpp *tfm) |
| 263 | +{ |
| 264 | + return CURVE25519_KEY_SIZE; |
| 265 | +} |
| 266 | + |
| 267 | +static struct kpp_alg curve25519_alg = { |
| 268 | + .base.cra_name = "curve25519", |
| 269 | + .base.cra_driver_name = "curve25519-ppc64le", |
| 270 | + .base.cra_priority = 200, |
| 271 | + .base.cra_module = THIS_MODULE, |
| 272 | + .base.cra_ctxsize = CURVE25519_KEY_SIZE, |
| 273 | + |
| 274 | + .set_secret = curve25519_set_secret, |
| 275 | + .generate_public_key = curve25519_generate_public_key, |
| 276 | + .compute_shared_secret = curve25519_compute_shared_secret, |
| 277 | + .max_size = curve25519_max_size, |
| 278 | +}; |
| 279 | + |
| 280 | + |
| 281 | +static int __init curve25519_mod_init(void) |
| 282 | +{ |
| 283 | + return IS_REACHABLE(CONFIG_CRYPTO_KPP) ? |
| 284 | + crypto_register_kpp(&curve25519_alg) : 0; |
| 285 | +} |
| 286 | + |
| 287 | +static void __exit curve25519_mod_exit(void) |
| 288 | +{ |
| 289 | + if (IS_REACHABLE(CONFIG_CRYPTO_KPP)) |
| 290 | + crypto_unregister_kpp(&curve25519_alg); |
| 291 | +} |
| 292 | + |
| 293 | +module_init(curve25519_mod_init); |
| 294 | +module_exit(curve25519_mod_exit); |
| 295 | + |
| 296 | +MODULE_ALIAS_CRYPTO("curve25519"); |
| 297 | +MODULE_ALIAS_CRYPTO("curve25519-ppc64le"); |
| 298 | +MODULE_LICENSE("GPL v2"); |
| 299 | +MODULE_AUTHOR("Danny Tsen <dtsen@us.ibm.com>"); |
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